1. Field of the Invention
This invention relates to a control device for an internal combustion engine which performs an optimum control of the internal combustion engine utilizing a hot-wire type air-flow sensor having a temperature dependent resistance.
2. Discussion of Background
FIG. 5 is a diagram showing a general construction of a control device for an internal combustion engine utilizing a hot-wire type air-flow sensor (hereinafter, AFS) having a temperature dependent resistance. In FIG. 5, a reference numeral 1 designates an air cleaner, 2, a hot-wire type air-flow sensor, 3, a throttle valve for controlling intake air quantity of an engine, 4, a surge tank, and 5, an intake (air sucking) manifold.
A numeral 6 designates an intake valve driven by a cam (not shown), and 7, a cylinder. Although only a portion of a single cylinder of the engine is shown in the diagram for simplification, the engine is actually composed of a plurality of cylinders.
A numeral 8 designates an injector in the respective cylinder 7, and 9, an electronic control unit (hereinafter, ECU) for controlling the fuel injection quantity of the injector 8 so that the fuel injection quantity and sucked air quantity compose a predetermined air fuel (A/F) ratio.
This ECU 9 determines the fuel injection quantity based on output signals of the AFS 2, a crank angle sensor 10, a starting switch sensor 11, and a cooling water temperature sensor 12 of the engine, and controls the fuel injection pulse width of the injector 8, in synchronism with the signal of the crank angle sensor 10.
The crank angle sensor 10 may be a well-known one which generates a square wave signal that falls at TDC (top dead center) and rises at BDC (bottom dead center) in the rotation of the engine.
FIG. 6 is a block diagram for explaining more in detail of the operation of the ECU 9. In a revolution number detecting unit 9a, the revolution number is obtained by measuring a period between TDCs of the square wave signal from the crank angle sensor 10. An average air quantity detecting unit 9b averages the output signal of the AFS 2, between TDCs of the square wave output signal of the crank angle sensor 10. In a basic pulse width calculating unit 9c, a basic pulse width is obtained by dividing an average air quantity output of an average air quantity detecting unit 9b, by a revolution number output of the revolution number detecting unit 9a.
A warming-up correcting unit 9d, determines a correction coefficient as for water temperature of the engine obtained by an output of the water temperature sensor 12. A correction calculation unit 9e performs the correction by adding or multiplying the correction coefficient to a basic pulse width which is obtained by the basic pulse width calculating unit 9c.
The starting pulse width calculating unit 9f calculates a starting pulse width which depends on the detected cooling water temperature of the engine. The switch 9g selects an injection pulse width or a starting pulse width in response to an output signal of the starting switch sensor 11 which detects the starting time of the engine. A timer 9h activates the pulse width in one shot operation at a timing when an output signal of the crank angle sensor 10 falls at TDC. An injector drive circuit 9i drives the injector 8.
FIG. 7 shows change of the intake air quantity at the starting time just after power ON, wherein the bold line curve A signifies the output signal of the AFS 2, the two dotted chain line curve shows the result of averaging the AFS signal between TDCs and corresponds to an output signal of the average air quantity detecting unit 9b, based on which the fuel injection quantity is calculated. The broken line curve C signifies an actual air quantity.
As shown in FIG. 7, it is known that the air quantity signal of the AFS 2 (curve A) just after power ON, exceeds the actual air quantity (curve C).
Since in the hot-wire type AFS, the air quantity is measured by detecting current flow through a temperature dependent resistance that is controlled at a constant temperature, and since the temperature dependent resistance is cooled down just after power ON, the resistance has to be heated to a predetermined temperature, which increases the current flow. Therefore, the air quantity signal of the AFS 2 becomes an abnormal value which is more than the actual air quantity.
Therefore, it is not possible to calculate the fuel injection quantity which is compatible with the actual air quantity, which lowers the controllability of the engine such as in deterioration of the exhaust gas.
Especially, in a hot-wire type AFS wherein platinum wire is wound around a ceramic bobbin, or in a hot-wire type AFS wherein platinum is vapor-deposited on an aluminum substrate or film, the time required for stabilizing the temperature dependent resistance to a predetermined temperature is long (for instance, several seconds) due to its temperature dependent resistance and heat conduction or heat accumulation to a retaining member, which is not negligible in view of the control of the internal combustion engine.
Since the control device for an internal combustion engine utilizing a conventional hot-wire type air-flow quantity sensor, is composed as above, and since the fuel injection quantity or the like is calculated based on the air-flow signal from the AFS, a control which is compatible with the actual air quantity can not be performed just after power ON.